Thiophene preparation from alkane and sulfur dioxide



Patented June 19, 1951 UNITED S'E'AEES QFFICE THIOPHENE PREPARATION FROMALKANE AND SULFUR DIOXIDE tion of Delaware No Drawing. Application June28, 1946, Serial No. 680,067

9 Claims.

'This invention relates to the production of heterocyclic sulfurcompounds and particularly to a method of producing organic compoundscontaining a thiophene nucleus such as thio- ,phene and the acyclichomologs thereof.

The utility and application of thiophene compounds, e. g., organiccompounds containing a thiophene nucleus, have in the past been re-'stricted in scope and were considered solely from the standpoint ofacademic interest, due to the fact that economic and commercial methodsof preparation were not available. Although various reactions have beenproposed for the preparation of thicphene and its compounds, suchreactions have been useful only for small scale laboratory preparations.

It has now been found that thiophene compounds can be synthesized from alarge class of reactants in accordance with a new and improved vaporphase catalytic process which is easily adapted to commercialoperations.

The process of the invention involves the reaction of a sulfur oxide andan alkane containing at least two carbon atoms in the presence of asolid contact catalyst at elevated temperatures with recovery of anorganic compound containing a thiophene nucleus from the reactionproduct. In general, the reaction process is conducted at temperaturesof at least 800 F., a space velocity (weights of alkane per hour perweight of catalyst) of at least 0.2 and a mol ratio of sulfur oxide toalkane of at least 0.5 to obtain optimum yields of thiophene compounds.It is to be understood that the particular thiophene compounds producedby the process are dependent to a large extent upon the choice of chargestock used in the reaction.

In accordance with the invention the process is especially applicable tothe production of thiophene itself or to thiophene compounds possessingacyclic substituents. Low molecular weight alkanes or parafiins, such asare produced from the processing of petroleum or natural gas, constitutesuitable charge stocks for the production of thiophene and the loweracyclic homologs. Such mixtures need not be separated to obtainindividual hydrocarbon components, but it is usually desirable to employa narrow fraction containing predominant amounts of alkanes having thesame number of carbon atoms. When alkanes containing more than fourcarbon atoms are used in the reaction, acyclic homologs of thiophene, inwhich the remaining carbon atoms are present in one or more side chains,are the predominant product.

The best yields of thiophene are obtained when a narrow butane cut isemployed and the best yields of methylthiophenes are obtained when thecharge stock is a narrow pentane cut. As examples of other hydrocarbonsthat may be employed as charge stocks there may be mentioned ethane,propane, hexanes, heptanes, etc. There appears to be no upper limit ofthe number of carbon atoms the alkanes may contain, although they shouldbe in vapor form under the reaction conditions. When relatively simplereaction products are desired, however, it is preferable to employ acharge stock containing prefur dioxide. The oxides are usually employedin a free state, but they may also be employed in the combined form,such as in the form of their hydrates. The hydrates, for example,decompose at the temperature of reaction to yield a charge mixturecomprising sulfur oxide and steam which serves as a diluent in thereaction mixture.

The heterocyclization reaction of the invention is conducted in thepresence of a solid contact catalyst which may be described chemicallyas a solid contact material of the class of oxides and sulfides whichare stable under the conditions of reaction. Such catalysts includemetal oxides which, under the conditions of reaction, may undergoconversion to the corresponding sulfide as, for example, molybdena. Itis recognized that certain of the materials classified as catalysts forthe subject reaction are relatively inert catalytically as applied toconventional hydrocarbon conversion reactions. Selection of theparticular catalysts to be used would depend to a large extent upon thechoice of charge stock used in the reaction. The solid contact catalystsusually preferred for general application with the majority ofeconomical charge stocks are the solid acid reacting catalysts, such assilica and the dehydrogenation catalysts. Specific examples of the typesof catalysts contemplated by the invention are silica, alumina, chromia,vanadia, molybdena, titania, magnesia, boria, molybdenum sulfide, nickelsulfide, tungsten sulfide, cobalt sulfide, tin sulfide, etc., as well asmixtures and chemical combinations thereof, such as silica-alumina,chromia-alumina, molybdenaalumina, acid-treated bentonitic clays, etc.

In carrying out the process of the invention the reactants in vapor formare introduced into a reaction chamber containing the solid contactcatalyst maintained at the desired reaction temperature. The catalyticreaction zone may be either a fixed bed type or a fluid type in whichthe catalyst is in a subdivided form and maintained in a turbulentsuspended state by the correct choice of catalyst particle size andspace velocity of the reactants. Since the reaction is exothermic, it ispreferable .to conduct the process in accordance with a fluid catalysttechnique which allows a greate control of the reaction temperature andimproved contact efiiciency of the reactants and catalyst.

It will be recognized that the conditions of reaction required to obtainoptimum yields of the particular thiophene compound desired will vary inaccordance with the particular reactants and catalyst employed as wellas the type of process technique. As a general proposition, however,temperatures in the range of 800 to 1500 F., a space velocity of 0.2 to6 weights of alkane per hour per weight of catalyst, and 2. mol ratio ofsulfur oxide to alkane within the range of 0.5 to 4, are preferred inthe majority of reactions.

The particular conditions of reaction are best illustrated by referenceto the conditions involved in the reactions of normal butane over a100-230 mesh chromia-alumina catalyst employing a fluidized fixed bedtype of process technique. When charging butane over a chromia-aluminacatalyst the space velocity should lie within the range of 0.5 to 1.5,with the mol ratio oi sulfur dioxide to butane in the range of 1.5 to2.5 and at a temperature of around 1100 to 1200 F. It is to beunderstood that the specific conditions described as optimum are thosewhich result in optimum yields of thiophene in a single pass operation.Where a continuous or recycled process is used, it may be desirable tomodify these conditions of reaction in order to obtain an optimumultimate yield of the desired product.

The catalyst activity for optimum thiophene production will depend tosome extent upon the charge stool: and reaction conditions employed, butwill generally be more than one hour. In any case, periodicdetermination of thiophene yields will indicate the practical period ofcatalyst activity before regeneration. When the catalyst yields arefound to fall off sharply the catalyst may then be regenerated forthiophene production by conventional methods typical of the type ofcatalyst technique employed.

The thiophene compounds produced by the reaction may be recovered fromthe reaction products in accordance with conventional methods ofextraction. For example, the reaction products which may compriseunreacted charge stocks, cracked products of the charge stock, olefiniccompounds, unreacted sulfur oxide and steam, may be passed through acaustic soda solution to dissolve the acid gases. If the caustic sodasolution is maintained cold the thiophene wil l condense in the form ofa separate layer.

The thiophene layer can then be drawn off and distilled. If the causticsoda solution is maintained hot the thiophene compounds will steamdistill from the caustic solution and can then be separated from thewater layer and purified by distillation. The thiophene compounds mayalso be recovered in crude form by a simple condensation procedure whichinvolves passing the. products into a cooled body of hydrocarbon oil,

such as kerosene, in which the thiophene compounds will condense andthen recovering the thiophene compounds by distillation.

It is evident that the process may be operated in accordance with any ofthe usual techniques for high temperature catalytic conversion. Thus,fixed catalyst beds may be used alternately in reaction and regenerationcycles; fluid catalyst operation may be used, with continuousregeneration and recycle of a powdered catalyst; fluidized fixed bedoperation may be used in which the catalyst particles remain in thereaction zone during alternate reaction and regeneration cycles.

The process of the invention may be further illustrated by the followingspecific examples:

Example I Normal butane and sulfur dioxide in a mol ratio ofapproximately 1.5 mols of sulfur dioxide per mol of butane were mixed,preheated to approximately 1100 F., and charged to a fluidized fixed bedreactor containing about 290 grams of a 40-100 mesh silica gel catalyst.The tem perature of the reaction zone was maintained at about 1100" F.and at substantially atmospheric pressure, with a space velocity ofapproximately 0.5 weight of butane per hour per weight of catalyst. Atwo-hour run was made during which time the thiophene recoveredrepresented a 37.3% by weight conversion of the butane charge.

Example II Normal pentane and sulfur dioxide in a mol ratio ofapproximately 0.9 mol of sulfur dioxide per mol of pentane were mixed,preheated and charged to a fixed bed reactor containing a commercialpelleted chromia-alumina catalyst containing approximately 10% chromia.The temperature in the reaction zone was maintained at an average of1015" F., with the pentane space velocity at approximately 0.75 weightof pentane per hour per weight of catalyst. The run was continued for aperiod of two hours and the products obtained represented a 6.3%conversion to 2-methyl thiophene and a 5.3% conversion to thiophene,based on the weight of the pentane charge.

Example III Isopentane and sulfur dioxide in a mol ratio ofapproximately 1.30 mols of sulfur dioxide per mol of isopentane weremixed, preheated and charged to a fixed bed reactor containing thechromia-alumina catalyst of Example II. The reactor temperature wasmaintained at an average of 1020 F., with the isopentane space velocityat approximately 1.0 weight of isopentane per hour per weight ofcatalyst. The run was continued for two hours during which time the perpass yield of thiophene and 3- methyl thiophene were 3.8 and 10.3%,respectively, with ultimate yields of 19.1 and 51. 1%, respectively,based on the weight of the isopentane charge.

Example IV 2,3-dimethyl butane and sulfur dioxide in a mol ratio ofapproximately one mol of sulfur dioxide per mol of hydrocarbon werecharged to a fixed bed reactor containing the chromiaalumina catalyst ofExample II. The temperature of the reactor was maintained at an averageof 1015" F. and the reactants charged at a space velocity ofapproximately 0.78 weight of 2,3-dimethyl butane per hour per weight ofcatalyst.

The run was continued for a period of two hours during which time theconversion to methyl thiophene and dimethyl thiophene represented aconversion of 2.2 and 11.8%, respectively, basis the hydrocarbon charge.

Example V Ethane and sulfur dioxide were mixed in a mol ratio of 1.9mols of sulfur dioxide per mol of ethane and charged to a fluidizedfixed bed reactor containing a chromia-alumina catalyst ground to100-200 mesh. The reactants were charged at a space velocity of 0.4weight of ethane per hour per weight of catalyst with the reactiontemperature maintained at 1400 F. The run was continued for about threehours during which time the thiophene recovered represented a per passconversion of 2.30% on the basis of the weight of the ethane charge.

It will be understood that these examples are merely illustrative of thepreferred embodiment of the invention and that other catalysts, chargestocks and specific conditions of reaction may be employed in accordancewith the previous description.

Obviously many modifications and variations. of the invention ashereinbefore set forth may be made without departing from the spirit andscope thereof, and only such limitations should be imposed as areindicated in the appended claims.

I claim: 1

1. A process for the production of a compound containing a thiophenenucleus which comprises passing sulphur dioxide and an alkane containingat least two carbon atoms at a space velocity between 0.2 and 6.0 weightof alkane per hour per weight of catalyst into .a reaction zonecontaining a solid contact catalyst, reacting said sulphur dioxide andsaid alkane in the vapor phase at a, temperature of at least 800 F. toform said thiophene compound and removing from said reaction zoneproducts of reaction containing said thiophene compound in substantialamount.

2. A process according to claim 1 in which the catalyst isacid-reacting.

3. A process according to claim 1 in which the alkane contains four toten carbon atoms.

4. A process for the production of a compound containing a thiophenenucleus which comprises passing sulphur dioxide and an alkane containingat least two carbon atoms at a space velocity of between 0.2 and 6.0weights of alkane per hour per weight of catalyst into a reaction zonecontaining a catalyst selected from the group consisting of metal andmetalloid oxides, sulfides and mixtures thereof stable under reactionconditions, reacting said sulphur dioxide and alkane in the vapor phaseat a temperature of at least 800 F. to form said thiophene compound andremoving from said reaction zone products of reaction containing saidthiophene compound in substantial amount.

5. A process according to claim 4 in which the reaction is effected at atemperature of about 1100 to 1200 F.

6. A process according to claim 4 in which the catalyst is a group VImetal oxide supported on a surface-active material.

7. A process according to claim 4 in which the catalyst is a group VImetal sulfide supported on a surface-active material.

8. A process for the production of a compound containing a thiophenenucleus which comprises passing sulphur dioxide and an alkane containingat least two carbon atoms at a space velocity of between 0.2 and 6.0weights of alkane per hour per weight of catalyst and at 3. mol ratio ofsulphur dioxide to alkane of at least 0.5 into a reaction zonecontaining a catalyst selected from the group consisting of metal andmetalloid oxides, sulfides and mixtures thereof stable under reactionconditions, reacting said sulphur dioxide and alkane in the vapor phaseat a temperature of at least 800 IE. to form said thiophene compound andremoving from said reaction zone products of reaction containing saidthiophene compound in substantial amount.

9. A process according to claim 4 in which the mol ratio of sulphurdioxide to alkane is between 1.5 to 2.5.

KENNETH L. KREUZ.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,126,817 Rosen Aug. 16, 19382,370,513 Amos Feb. 27, 1945 2,418,374 Stone Apr. 1, 1 947.

1. A PROCESS FOR THE PRODUCTION OF A COMPOUND CONTAINING A THIOPHENENUCLEUS WHICH COMPRISES PASSING SULPHUR DIOXIDE AND AN ALKANE CONTAININGAT LEAST TWO CARBON ATOMS AT A SPACE VELOCITY BETWEEN 0.2 AND 6.0 WEIGHTOF ALKANE PER HOUR PER WEIGHT OF CATALYST INTO A REACTION ZONECONTAINING A SOLID CONTACT CATALYST, REACTING SAID SULPHUR DIOXIDE ANDSAID ALKANE IN THE VAPOR PHASE AT A TEMPERATURE OF AT LEAST 800* F. TOFORM SAID THIOPHENE COMPOUND AND REMOVING FROM SAID REACTION ZONEPRODUCTS OF REACTION CONTAINING SAID THIOPHENE COMPOUND IN SUBSTANTIALAMOUNT.